Vox VT100 DSP amp, 2008

[N_Cook]

Loss of bass output, low level compared to mid and treble input test
signals. Altering bass pot makes little difference in output level with bass
test signal and marginal max is near the centre. I've not traced the bass
pot back to a DSP area yet. Bass and other pots are not broken/worn and
solder seems ok . This is PbF/RoHS and Korg era.
Anyone know how much circuitry is common to the Korg/Vox AD100VT schematic ?
or a schematic perhaps for the VT100 . Same o/p STK404-130S and
"valvetronix" low-voltage LED-lit valve fudge (whats the point of DSP if you
don't emulate valve function?) but different op-amps types at least.
This is a DSP amp with dedented pots for rotary function switch action so
expect future problems there.

 

[N_Cook]

initial continuity checking from pot wiper to pin 60 of the M3803 seemed to
show a break, subsequent checking showed ok, x30 viewing looks ok , pin
sounding sounded ok, but have assumed PbF failure , resoldered the .5mm
spacing pin with solder paste, viewed for bridges and reassembled and then
power up with fingers crossed.
AD100VT schema has the bass pot wiper line going to pin61 so only similar in
that area

 

[N_Cook]

What a pig's ear of an amp. There was also PbF failure at the input socket,
reported by the owner. I don't know what they are called but .1 inch spacing
IDC "header" for discrete wire "ribbon" soldering to a pcb. Re-work of one
by the maker, by soldering over the IDC points very messily. Another such
pcb fixing had failed at an IDC causing intermittent signal dip , I marked
and cut the wires and soldered individually to the pcb. The nuts , with no
star washers, were loose , holding the o/p STK404 to the h/s. Usual suspect
PbF solder points delt with. Now to lay bets on when this amp will bounce
back with more problems, only 4 years old. My guess would be that the click
switches are far too sensitive for use on combos and will self-activate from
vibration before long